题目

    I am Peter Hodes, a volunteer stem courier. Since  March 2012, I've done 89 trips of those , 51 have been abroad, I have 42 hours to carry stem cells（干细胞）in my little box because I've got two ice packs and that's how long they last, in all, from the time the stem cells are harvested from a donor(捐献者) to the time they can be implanted in the patient, we’ve got 72 hours at most, So I am always conscious of time. I had one trip last year where I was caught by a hurricane in America. I picked up the stem cells in Providence, Rhode Island, and was meant to fly to WasJack was busy ___________ his homework and his sister Rose was busy ___________ the house work.A.do… withB.doing… withC.do… onD.doing… on